Remote sensing upscaling of interception loss from isolated oaks: Sardon catchment case study, Spain

Tree interception loss from two Mediterranean oak species, Quercus ilex (Q.i.) and Quercus pyrenaica (Q.p.), was estimated during 2-year period (1 October 2011 to 30 September 2013) in sparsely vegetated Sardon catchment (∼80 km2, Spain) by: i) rainfall, throughfall and stemflow measurements; ii) Gash model temporal extrapolation; and iii) remote-sensing spatial upscaling. The annual, measured tree interception losses (Im) of Q.i. and Q.p. in the first year were 51% and 16% of P (335 mm) and in the second, 46% and 10% of P (672 mm), respectively. The revised Gash analytical model of rainfall interception loss, extrapolated well the Im temporal variability of Q.i. and Q.p., provided the throughfall-based, and not Pennman-Monteith-based, average wet canopy evaporation rates were used. Finally, a novel method of spatial upscaling of a tree-based interception loss into plot- and catchment-scale, using per-species, reference tree interception loss and object-attributes derived from satellite imagery, was proposed. The interception losses from Q.i. and Q.p. were upscaled first into two homogeneous plots (1-ha each and both with ∼20% canopy cover), one with Q.i. and the other with Q.p. oaks and then into the entire Sardon catchment with ∼7% canopy cover. The obtained annual-mean, plot interception losses were 9.5% of P in evergreen Q.i. and 2.5% of P in deciduous Q.p. plot. The annual-mean catchment interception loss was 1.4% of P. The proposed upscaling method is expected to improve catchment water balances, replacing common arbitrary or literature based tree interception loss estimates.